Reforming and isomerization process, with dehydrogenation of unconverted light paraffins



United States Patent O REFORMING AND ISOMERIZATION PROCESS,

WITH DEHYDROGENATION F UNCON- VERTED LIGHT PARAFFINS La Vern H. Beckberger, Harvey, Ill., assignor to Sinclair Refining Company, New York, N. Y., a corporation o1 Maine Application February 17, 1953, Serial No. 337,356 Claims. (Cl. 208-65) This application relates to a two-stage process for catalytic conversion of petroleum hydrocarbon fractions boiling within the gasoline range. More particularly it relates to a process in which a mixture of naphtha and a normal paraflin are charged to the rst stage to produce a typical reformate and to obtain partial conversion of the normal paraiiin to an isoparaffin and in which the unconverted normal paraflin is charged to a second stage to produce the corresponding normal olefin.

This application is a continuation-in-part of my copending application Serial No. 245,750, filed September 8, 1951, and is directed to a method of operation in which a mixture of 300 to 375 F. boiling range naphtha and a light normally gaseous normal parain fraction, such as n-butane and n-pentane or mixtures thereof, are contacted in a first reaction stage with a reforming catalyst in the presence of hydrogen under reforming conditions of temperature, pressure and space velocity to produce a typical reformate while eifecting partial conversion of the normal paraflin fraction, e. g. about 25 percent conversion, to an isoparatlin fraction. In the second stage the unconverted portion of the normal paraffin fraction is contacted with a chromium oxidealumina catalyst under dehydrogenation conditions of space velocity and elevated temperature including subatmospheric pressure to approximately atmospheric pressure to produce a normal olefin fraction. The isoparain fraction and the normal olefin fraction may then be charged to an alkylation unit.

The first stage conditions advantageously approximate 500 p. s. i. g. total pressure, -1 gas recycle mole ratio, 900 F., 4 LHSV naphtha, 2 LHSV normal paraffin. In the second stage the conditions may be as high as one atmosphere total pressure, 1000 gas hourly space velocity for the normal parain feed and 1050 F. for a 10 minute hydrocarbon recycle operation. The hydrogen partial pressure for the first reaction stage is advantageously provided by recycle of hydrogen rich tail gases from the process.

Flexibility and selectivity are provided to a high degree by division of the catalytic conversion reactions into step-wise and selectively conducted isomerizationdehydrogenation reactions in the iirst stage and dehydrogenation reactions primarily in the second stage. In this respect, chromium oxide-alumina reforming catalysts of the type known to the art, which contain about 10 to 12 percent chromium oxide, have special advantage in a low pressure high temperature reaction combined with a preceding reforming operation. The reforming operation lends itself to the use of a number of catalysts, but with advantage is conducted with a platinum type reforming catalyst such as the platinum-alumina-halide catalyst described in Haensel Patent 2,479,110 or the platinumalumina-silica catalyst of Ciapetta Patent 2,550,531. Also molybdenum oxide-alumina reforming catalysts are useful and particularly the molybdenum oxide-aluminasilica type catalysts when promoted by addition of a ,small amount of oxygen or air to the hydrogen gas stream A2,862,872 Patented Dec. 2, 1958 2 as described in application Serial No. 236,792, tiled July 14, 1951, now U. S. Patent No. 2,661,320, of LaVern H. Beckberger and Rudolph E. Woerner. Other reforming catalysts of value are tungsten-nickel sulfide, zinc-magnesia molyblenum oxide, vanadia-chromia on alumina.

According to the particular aspects of my invention represented by the figure, a naphtha feed stock is charged by means of line 9 and n-butane for example, is charged by means of line 10 through pump 11 and line 12 to heater 13. From the heater the vaporzed feed is passed through reactor 14, reheater 15 and reactor 16. Because of the endothermic reaction it is advantageous to provide for multi-stage reaction by intermediate reheating of the reaction mixture. At the inlet to heater 13, the naphtha "ice . feed and n-butane in line 12 is admixed with hydrogen rich tail gas recycled from the reaction through line 17. Reactors 14 and 16 are charged with a reforming catalyst, advantageously in pelleted or tableted form, disposed as a fixed bed. The efuent from reactor 16 is withdrawn through line 18 and is passed through cooler 19 to separator 20. A liquid fraction is withdrawn through valved connection 21 and passed through heater 22 to stabilizer 23. A liquid fraction is withdrawn from stabilizer 23 and passed to the usual fractionation system for segregation of aromatic products or high octane gasoline. Gas separated in stabilizer 23 is passed to fractionator 24 where the C3 and lighter and C4 and heavier fractions are separated. Gas separated in separator 20 and fractionator 24 is removed respectively through lines 25 and 26 which may be connected by valved line 27. Hydrogen rich tail gas for recycle is returned to the process by line 28, compressor 29 and line 17. The C., and heavier fraction is withdrawn from fractionator 24 through line 30 and passed to separator 31 where the iso-butane is separated from the n-butane. Iso-butane is withdrawn through line 32. N-butane is withdrawn through line 33 and passed to heater 34.

The heated n-butane is then passed to the onstream reactor of the pair of adiabatic fixed bed type reactors 35 and 36 by means of connection 37, selection valve system 38 and one of connections 39 or 40. The efuent from the onstream reactor is withdrawn by one of the connections 41 or 42 and selection valve system 43 to line 44 and cooler 45. The cooled stream is then passed serially through a system of gas-liquid separators and compressors comprising flash drum 46, compressor 47, flash drum 48, compressor 49 and ash drum 50. The flashed gas may be passed through absorber 51 from which non-condensible gas is removed by line 52 and from which condensed or absorbed liquid components are removed by line 53. The liquid product in line 53 is combined with .the liquid fractions recovered in the separation and compressor stages and collected in line 54 and the combined liquid product stream is passed to the usual fractionation system for segregation of n-butylene.

Reactors 35 and 36 are provided with pelleted chromium oxide-alumina catalyst in bed form. The catalyst is cyclically regenerated by switching the ow after a period of hydrocarbon processing to a ow of a regeneration gas containing air and flue gas. The air stream is advantageously diluted with flue gas to prevent excessively high temperatures during regeneration. Advantageously, each cycle is preceded by evacuation and then a short purge period during which ue gas is passed through the catalyst bed. As shown in the drawing, air may be supplied by blower 55 and lines 56 and 57 through heat exchanger 58 and line 59 to selection valve system 38 from where it is directed to the appropriate reactor 35 or 36 which is undergoing regeneration. Flue gas is withdrawn by line 41 or 42 to selection valve 3 system 43 and is passed by means of line 60 through heat exchanger 68. Flue gas for purge and regeneration may be supplied by blower 6'1", line 62 and thence through the regeneration Vair szys'ter'. A

By way of illustration `of the Voperation 'of Figre 1*, a 200 to 375 F. naphtha'andn-'butanerhay be ch'arg'ed to the first stage. The rst stage `conditions 'advantageously approximate S p. s. i. g. total pressure, 10/1 gas recycle mole ratio, 900 F., 4 LHSV naphtha 'and 2 LHSV n-but'ane. Instead of n-butane, n-pentane or mixtures of Ythe two vmay be employed. A typical rcformate 'and isobutane Yrepresenting about'a 25 percent conversion of n-butane are produced in the first stage and separated from its eflluent. In the second `s'tagefthe unconverted butane is converted to 'rl-butylene. In this second stage, the conditions may be as high as -one atmosphere total pressure, 1000 gas hourly space velocity for the n-butane feed and 1050 F. for 10 minute hydrocarbon process period.

I claim:

1. A two-stage process for the catalytic conversion of hydrocarbon Ifeed stocks boiling within the gasoline range which comprises contacting a mixture `of such a stock and a material consisting essentially o'f a light normally gaseous normal C4 to C5 paraffin fraction in a first reaction stage with a reforming lcatalyst iii 'the presence of hydrogen under reforming conditionsof temperature, pressure and space velocity, separating 'gas and liquid fractions from the reaction effluent, withdrawing the liquid fraction, separating isoparain from the uncon'- verted normal parain in the gas fraction, withdrawing the isoparafiin fraction, contacting `the unconve'rted normal paraffin fraction with a chromium oxide-alumina catalyst under dehydrogenation conditions of space velocity and elevated temperature including sub-atmospheric to approximately latmospheric pressure, and separating a normal olen fraction from the second stage reaction efuent.

2. The process of claim 1 in which hydrogen rich gas separated in the course 4of the process provides by recycle the hydrogen for the rst stage reaction.

3. The process of claim 1 in which the rst stage reaction is conducted in the presence of a platinum-type reforming catalyst.

4. The process of claim 1 in which the first stage reaction is conducted in the presence of a molybdenum oxide-'alumina type reforming catalyst.

5. The process of claim 1 in which the feed stock comprises a mixture of a 200 to 375 F. straight run naphtha and n-butane, and from which an aromatic rich liquid fraction is ultimately recovered from Athe rst stage reaction effluent and n-butylene is ultimately recovered from the second stage reaction effluent.

References Cited in the file of this pate-nt UNITED STATES PATENTS 

1. A TWO-STAGE PROCESS FOR THE CATALYTIC CONVERSION OF HYDROCARBON FEED STOCKS BOILING WITHIN THE GASOLINE RANGE WHICH COMPRISES CONTACTING A MIXTURE OF SUCH A STOCK AND MATERIAL CONSISTING ESSECTIALLY OF A LIGHT NORMALLY GASEOUS NORMAL C4 TO C5 PARAFFIN FRACTION IN A FIRST REACTION STAGE WITH A REFORMING CATALYST IN THE PRESENCE OF HYDROGEN UNDER REFORMING CONDITIONS OF TEMPERATURE, PRESSURE AND SPACE VELOCITY, SEPARATING GAS AND LIQUID FRACTIONS FROM THE REACTION EFFLUENT, WITHDRAWING THE LIQUID FRACTIONS, SEPARATING ISOPARAFFIN FROM THE UNCOM- 